Add StudyGroup to submissions and show it for submissions and RfCs

Also take care of deleting a StudyGroup for existing submissions

app/controllers/request_for_comments_controller.rb

@@ -83,17 +83,10 @@ class RequestForCommentsController < ApplicationController
     authorize!
   end
 
-  # GET /request_for_comments/new
-  def new
-    @request_for_comment = RequestForComment.new
-    authorize!
-  end
-
   # GET /request_for_comments/1/edit
   def edit
   end
 
-  # POST /request_for_comments
   # POST /request_for_comments.json
   def create
     # Consider all requests as JSON
@@ -149,8 +142,8 @@ class RequestForCommentsController < ApplicationController
 
     # Never trust parameters from the scary internet, only allow the white list through.
     def request_for_comment_params
-      # we are using the current_user.id here, since internal users are not able to create comments. The external_user.id is a primary key and does not require the consumer_id to be unique.
-      params.require(:request_for_comment).permit(:exercise_id, :file_id, :question, :requested_at, :solved, :submission_id).merge(user_id: current_user.id, user_type: current_user.class.name)
+      # The study_group_id might not be present in the session (e.g. for internal users), resulting in session[:study_group_id] = nil which is intended.
+      params.require(:request_for_comment).permit(:exercise_id, :file_id, :question, :requested_at, :solved, :submission_id).merge(user_id: current_user.id, user_type: current_user.class.name, study_group_id: session[:study_group_id])
     end
 
     def comment_params